Noise Analysis And Simulation Test Research For Pod Vibration Of Helicopter-borne TEM System

Helicopter-borne Time-domain Electromagnetic Method (HTEM) is a kind ofresource detection method on the carrier of helicopter. It completes resourceexploration during the flight. Compared with other airborne electromagnetic method,it is fast, mobile and flexible, suitable for exploration in complex terrain areas.Currently this method has been widely used in mineral resources exploration, waterresources exploration, geological mapping, environmental monitoring and other fieldsin overseas, and it has made a series of achievements. The principle ofHelicopter-borne Time-domain Electromagnetic Method is same to conventionalground time domain electromagnetic method, by observing the secondary field decaycurve to discriminate subsurface structure. The data SNR is low, susceptible to affectby external noise environment. Traditional filtering methods are mostly limited tonoise filtering by way of software, because of the randomness of the state of motion.It has a strong human intervention data factors affecting the reliability of the data.Exploring the evaluation of the effects of noise from the source of movement motionhas important significance of the elimination of motion essentially.On the basis of introducing the principle of Helicopter-borne Time-domainElectromagnetic Method and vibration measurement method, electromagneticinduction voltage simulation caused by pod vibration and design of helicoptertime-domain electromagnetic detection system pod vibration test equipment are putforward. The following describes the contents of the main study.Based on the analysis of sources of the motion noise, vibration of the mechanicalstructure of the pod is simulated by ANSYS Workbench. The mechanical vibrationposition is given by modal analysis. The changed trend of dramatic points is analyzedunder the influence of different frequency. Then the options of accelerometer fixedlocation are proposed. Pod attitude change caused by vibrations will generate voltagenoise, it is simulated by ANSYS Maxwell. There is an angle between the transmittercoil and the receiving coil, the transmitter coil and the receive coil are parallel but notcoplanar, mutual inductance formulas are fitting out of both cases. The inducedvoltage noise formula is deduced from mutual inductance Analyze the noise voltagefunction of the receiver coil swing in the geomagnetic field. Multiple vibration points decomposed to a single point vibration for pod structure, formula of projection areachange of transmitter coil in the receiving coil plane caused by single point vibrationis deduced，it provide a basis for further study of the relationship between projectionarea change and induction noise voltage of receiving coil.Using three axial acceleration sensor， the pod vibration test equipment for thehelicopter-borne time-domain electromagnetic detection system is designed based onthe NI CompactDAQ9139and NI9239acquisition cards. With GPS second pulseand current waveform as the dual synchronization scheme. Power supply conversioncircuit is designed. Software state machine is used as the heart of the LabVIEWprogram. Realizing the work mode of multitasking, data storage is in binary format.The characteristics of multi-channel, large storage, synchronization acquisition areachieved， performance meet the needs of pod vibration testing for thehelicopter-borne time-domain electromagnetic detection system.The pod model device and laboratory simulation experiment platform are made.Analyzed the angle of initial state of three axial acceleration sensor. Wavelet decreasenoising principle is introduced, the wavelet analysis results of acceleration signalshow that the processing method is reliable. Three groups of experiment are designed,vibration test results of the vibration test equipment show that vibration testequipment can reliable work, the measured results are consistent with the simulation,it has certain reference value to guide the research of motion noise subsequently.